1. Field of the Invention
The present invention relates to an optical film, particularly, a brightness enhancement film for use in liquid crystal displays.
2. Description of the Prior Art
Conventionally known backlight modules for liquid crystal displays (LCDs) mainly utilize diffusion plates, diffusion films, and light-gathering films to achieve the purposes of homogenizing and gathering light. The main function of the diffusion plates and diffusion films is to provide liquid crystal displays with a uniform surface light. The main function of a light-gathering film, also referred to as brightness enhancement film or prism film in the industry, is to gather the scattered light rays in all directions by refraction and internal total reflection and converge the light rays in the on-axis direction of about ±35 degrees to enhance the luminance of LCDs. Normally, the brightness enhancement film achieves the effect of gathering light by means of regularly or irregularly arranged linear prismatic structures.
FIG. 1 is a schematic diagram of a conventional brightness enhancement film (as disclosed in PCT 96/23649 and U.S. Pat. No. 5,626,800). As shown in FIG. 1, the brightness enhancement film comprises a substrate 1 and a plurality of prism structures 2 on the substrate 1; the prism structures are parallel to each other and each prism structure is composed of two slant surfaces, where the two slant surfaces meet at the top of the prism to form a peak 3, and each surface meets with the another slant surface of an adjacent prism to form a pit 4.
In order to further integrate the light-gathering and light-diffusion functions, as shown in FIG. 2, U.S. Pat. No. 6,280,063 discloses a brightness enhancement film 20 which comprises a substrate 22, linear columnar structures having blunted and rounded peaks 26 on one side of the substrate 22, and irregular diffusion materials 24 on the other side of the substrate 22, as so as achieve the purposes of gathering and homogenizing light.
It is known that the refracted light rays from the brightness enhancement film having regularly arranged columnar structures will optically interfere with the refracted or reflected light rays from other films of the displays or with other light rays refracted or reflected by the brightness enhancement film itself, thereby resulting in Moiré or Newton ring in appearance. TW Patent No. M291542 discloses serpentine optical adjustment elements for reducing the light interference and achieving the purposes of gathering and homogenizing light. As shown in FIG. 3(a) and FIG. 3(b), the serpentine optical adjustment element comprises a substrate 31 and serpentine microstructures 33, where the substrate 31 has a first optical surface 311 and a second optical surface 313, and the serpentine microstructures 33 are arranged on the first optical surface 311 and have a diffusion part 331 and light-gathering part 333. FIG. 3(b) shows a top view of the serpentine optical adjustment element of FIG. 3(a). As shown in FIG. 3(b), the diffusion part 331 and light-gathering part 333 are in the form of continuously bending curves so as to alleviate optical interference.
It is known that when the prism structures of the brightness enhancement film are in contact with panels or other optical films, scratching tends to occur, thereby affecting the optical properties. Presently, the main solution adopted in the industry is to use a protective diffusion film (which is also referred to as an “upper diffusion film”) to avoid the impairment between the brightness enhancement film and the panels or other optical films caused by the vibration during transportation. In addition to utilizing the protective diffusion film to avoid the scratching caused by the contact between the brightness enhancement film and the panels, before packaging, it is necessary to adhere a protective film onto the brightness enhancement film to avoid the impairment caused during the storage and/or transportation of the brightness enhancement film. Nevertheless, the utilization of a protective diffusion film and protective film will increase the cost. Although the linear columnar structures having blunted and rounded peaks disclosed in the above-mentioned U.S. Pat. No. 6,280,063 may reduce the impairment of the brightness enhancement film caused by the contact between the prism structures of the brightness enhancement film and other films or panels and enhance the abrasion resistance property, the light-gathering effect of blunted and rounded columnar structures is not as good as that of prism columnar structures. Although TW Patent No. M291542 discloses optical adjustment elements having arc columnar structures (i.e., the diffusion part) and prism columnar structures (i.e., the light-gathering part) to achieve the purposes of gathering and homogenizing light, as discussed above, however, the prism columnar structures are easy to be scratched due to the contact with other films or panels and the abrasion resistance property is poor.
Given the above, the present invention provides an optical film to obviate the above-mentioned shortcomings. The present invention alleviates the scratch caused by the contact between the optical film and other optical films or panels and can reduce the cost associated with any upper diffusion film or adhered protective film.